Albert Barnes Commentary 1 Kings 18:33

"And he put the wood in order, and cut the bullock in pieces, and laid it on the wood. And he said, Fill four jars with water, and pour it on the burnt-offering, and on the wood." — 1 Kings 18:33 (ASV)

And he put the wood in order... - In other words, he obeyed all the requirements of the Law regarding the offering of a burnt sacrifice. In this way, he publicly taught that the ordinances of the Law were binding on the kingdom of Israel.

Barrels - This refers to “pitchers” or “water-jars,” like the ones young women used to carry on their heads (Genesis 24:14–20; compare to Judges 7:16, 19). Flooding the sacrifice and the trench with water would immediately eliminate any suspicion of fraud and greatly enhance the wonder of the miracle in the eyes of the people. The unfailing spring at the eastern end of Carmel could provide as much water as he needed (1 Kings 18:19).